How clathrin-coated pits control nanoparticle avidity for cells

The paramount relevance of clathrin-coated pits (CCPs) to receptor-mediated endocytosis of nanoparticles, extracellular vesicles, and viruses has made them the focus of many studies; however, the role of CCP geometry in the ligand-receptor interactions between multivalent nanoparticles and cells has not been investigated. We hypothesized the general dependence of nanoparticle binding energy on local membrane curvature to be expandable to the specific case of ligand-functionalized nanoparticles binding cell membranes, in the sense that membrane structures whose curvature matches that of the particle (e.g., CCPs) signficantly contribute to binding avidity. We investigated this hypothesis with nanoparticles that bind multivalently to angiotensin II receptor type 1, which is subject to clathrin-mediated endocytosis. When we used cholesterol extraction to prevent the action of CCPs, we found a 67 to 100-fold loss in avidity. We created a theoretical model that predicts this decrease based on the loss of ligand-receptor interactions when CCPs, which perfectly match nanoparticle geometry, are absent. Our findings shed new light on how cells "see" nanoparticles. The presence or absence of CPPs is so influential on how cells interact with nanoparticles that the number of particles required to be visible to cells changes by two orders of magnitude depending on CCP presence.